Instruments for measuring the thicknesses of aerospace skins and related supporting structures exist in the prior art. In most instances, those instruments enable a user to measure the thickness of an aircraft skin and its supporting structure while having access to only one side of the skin. In U.S. Pat. No. 2,293,411 to Spillmann, a thickness gauge is described which includes a hook shaped portion that is extendable through an opening in the skin of a closed structure and is adapted to engage the hidden side of the skin. A secondary probe is movable to bear upon the outer surface of the skin, to thereby enable a measurement to be taken indicating the thickness of the skin.
In U.S. Pat. No. 4,237,612 to Christian et al., a similar measuring instrument is described which measures a skin thickness and determines a corresponding fastener grip length. Christian et al. describes a measuring structure similar to that shown by Spillmann, but rather employs an electronic system rather than the mechanical device shown by Spillmann. Christian et al. employ a hook shaped probe, around which is mounted a slidable, outer-skin probe. When the hooked probe is inserted in an opening and is hooked onto the hidden (inner) surface of the skin, the slidable outer probe bears upon the outer surface of the skin. Attached to the slidable probe is a wiper which passes over a commutator-like structure within the instrument. As the wiper makes contact with each commutator bar, an indication is provided of the size fastener required for the particular measurement. Thus, the user must, after each measurement, either make note of the required fastener or have a supply of all size fasteners available for immediate use.
An electronic measuring apparatus is disclosed in U.S. Pat. No. 4,612,656 to Suzuki et al., and shows a caliper-like structure having a digital read out which is fed to a printer where each measurement may be individually recorded. While the printout of a series of measurements is useful, neither Suzuki, Spillmann, or Christian et al. solve certain problems which are extant in a manufacturing facility. It is often impractical to maintain a supply of a wide variety of fastener lengths at every workstation. Furthermore, it is difficult to anticipate the numbers of each size fastener which will be required at a particular work station as production proceeds. Finally, having to pause after each measurement, find the proper fastener and then insert it, is a time consuming process which is labor-inefficient.
Accordingly, it is an object of this invention to provide a portable measuring system which automatically converts skin measurements to standard fastener sizes.
It is still another object of this invention to provide a portable measuring system which enables more efficient utilization of assembly labor than heretofore.
It is yet another object of this invention to provide a portable measuring system that enables a precise prediction of the number and types of standard fastener sizes required for a series of measurements, and further associates each measurement with a particular standard fastener size.